In recent years, there has been a increasing interest in a class of materials commonly referred to as ferroelectric materials which have found wide use in random access memory applications. In such applications, it has been common to employ ferroelectric capacitors which typically evidence high remanent polarization, small size, low leakage current and low fatigue rate. Accordingly, workers in the art have focused their interest upon the development of suitable techniques for the growth of ferroelectric thin films with optimum characteristics.
Among the earliest materials investigated for such applications were the perovskite ferroelectrics such as PbZr.sub.1-x Ti.sub.x O.sub.3, commonly known as PZT. Unfortunately, the techniques employed for the preparation of these materials have resulted in the formation of defects which alter the stoichiometry due to the creation of vacancies. As a result of these difficulties, degradation problems such as fatigue, aging and leakage currents which adversely affect the device lifetime often occur.
More recently, workers in the art focused their interest upon the preparation of SrBi.sub.2 Ta.sub.2 O.sub.9 (SBT) films using metallorganic vapor deposition techniques. Thus, for example, Desu et al. in U.S. Pat. No. 5,527,567 disclosed a method for the deposition by chemical vapor deposition techniques of high quality layered structured oxide ferroelectric thin films. These films were deposited at temperatures ranging from 450-800.degree. C. The patentees specifically noted that at temperatures greater than 650.degree. C. poor quality films were produced whereas at temperatures less than 600.degree. C. excellent quality films were obtained. However, the use of the lower temperatures was found to lower the deposition rate, thereby necessitating a two step deposition with a short term deposition at temperatures ranging from 450-600.degree. C. and a longer term deposition at temperatures ranging from 600-700.degree. C.
Desu et al. further discovered that in the one step deposition procedure using high temperatures, heterogeneous nucleation and grain growth frequently occurred on the polycrystalline material employed as the bottom electrode in the capacitor of interest. The films so produced evidenced a non-uniform crystalline structure having a rough surface morphology. The patentees found, however, that in the two step deposition process, the first step yielded a thin uniform nucleation layer with grain growth occurring at the top of the substrate which provided a homogeneous nucleation and grain growth condition for the second deposition step.
Although this prior art technique and related techniques described by workers in the art have enjoyed a limited level of success, they have not proven satisfactory in depositions involving the use of multiple substrates. Thus, for example, if two substrates such as platinum and silicon dioxide are present in a chemical vapor deposition process for the preparation of ferroelectric SBT thin films, deposition will occur on both substrates. The deposition of bismuth oxide adjacent to an electrode at high temperatures is undesirable because of the ability of bismuth to migrate into the substrate and react with the components of the substrate. Unfortunately, this end negates the ability to use such techniques for the deposition of ferroelectric media suitable for use in ferroelectric random access computer memories.